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In the paper the algebra of invariants of the adjoint action of the unitriangular group in the nilradical of a parabolic subalgebra is studied. We set up a conjecture on the structure of the algebra of invariants. The conjecture is proved…

Representation Theory · Mathematics 2012-05-15 Victoria Sevostyanova

In this work we present a new definition to the Partial Crossed Product by actions of inverse semigroups in a C^*-algebra, without using the covariant representations as Sieben did in [5]. Also we present an isomorphism between the partial…

Operator Algebras · Mathematics 2008-05-26 Ruy Exel , Felipe Vieira

We study free and compact group actions on unital C*-algebras. In particular, we provide a complete classification theory of these actions for compact Abelian groups and explain its relation to the classical classification theory of…

Operator Algebras · Mathematics 2025-12-24 Kay Schwieger , Stefan Wagner

This paper studies the class group of graded integral domains. As an application, we state a decomposition theorem for class groups of semigroup rings. This recovers well-known results developed for the classic contexts of polynomial rings…

Commutative Algebra · Mathematics 2007-05-23 S. El Baghdadi , L. Izelgue , S. Kabbaj

We consider partially hyperbolic abelian algebraic high-rank actions on compact homogeneous spaces obtained from simple indefinite orthogonal and unitary groups. In the first part of the paper, we show local differentiable rigidity for such…

Dynamical Systems · Mathematics 2009-10-28 Zhenqi Wang

We give a new characterization of partial groups as a subcategory of symmetric (simplicial) sets. This subcategory has an explicit reflection, which permits one to compute colimits in the category of partial groups. We also introduce the…

Group Theory · Mathematics 2025-03-10 Philip Hackney , Justin Lynd

The main notions of the quantum groups: coproduct, action and coaction, representation and corepresentation are discussed using simplest examples: $GL_q(2)$, $sl_q(2)$, $q$-oscillator algebra ${\cal A}(q)$, and reflection equation algebra.…

q-alg · Mathematics 2016-09-08 E. V. Damaskinsky , P. P. Kulish

Given a finite alphabet $\Lambda$, and a not necessarily finite type subshift $X\subseteq \Lambda^\infty$, we introduce a partial action of the free group $F(\Lambda)$ on a certain compactification $\Omega_X$ of $X$, which we call the…

Operator Algebras · Mathematics 2015-11-04 M. Dokuchaev , R. Exel

Let $\mathbb{F}_q$ be the finite field with $q$ elements, where $q$ is a power of a prime $p$. Recently, a particular action of the group $\mathrm{GL}_2(\mathbb F_q)$ on irreducible polynomials in $\mathbb F_q[x]$ has been introduced and…

Rings and Algebras · Mathematics 2017-09-15 Lucas Reis

We investigate compact quantum group actions on unital $C^*$-algebras by analyzing invariant subsets and invariant states. In particular, we come up with the concept of compact quantum group orbits and use it to show that countable compact…

Operator Algebras · Mathematics 2015-11-17 Huichi Huang

This paper proves various results concerning non-ergodic actions of locally compact groups and particularly Borel cocycles defined over such actions. The general philosophy is to reduce the study of the cocycle to the study of its…

Dynamical Systems · Mathematics 2007-05-23 D. Fisher , D. Morris , K. Whyte

Let G be an algebraic group over a complete separable valued field k. We discuss the dynamics of the G-action on spaces of probability measures on algebraic G-varieties. We show that the stabilizers of measures are almost algebraic and the…

Group Theory · Mathematics 2021-02-03 Uri Bader , Bruno Duchesne , Jean Lécureux

Various kinds of infinitary operations satisfying forms of associativity have been considered in the literature by various authors, including A. Tarski, C. Karp, J. H. Conway, D. Krob, N. Bedon, and C. Rispal. Applications include the…

Group Theory · Mathematics 2026-05-28 Paolo Lipparini

We consider an arbitrary representation of the additive group over a field of characteristic zero and give an explicit description of a finite separating set in the corresponding ring of invariants.

Commutative Algebra · Mathematics 2013-02-05 Emilie Dufresne , Jonathan Elmer , Müfit Sezer

Two types of recurrence sets are introduced for inverse semigroup partial actions in topological spaces. We explore their connections with similar notions for related types of imperfect symmetries (prefix inverse semigroup expansions,…

Dynamical Systems · Mathematics 2021-02-17 Marius Mantoiu

We study generalized group actions on differentiable manifolds in the Colombeau framework, extending previous work on flows of generalized vector fields and symmetry group analysis of generalized solutions. As an application, we analyze…

Functional Analysis · Mathematics 2007-06-12 Sanja Konjik , Michael Kunzinger

We introduce semiframes (an algebraic structure) and investigate their duality with semitopologies (a topological one). Both semitopologies and semiframes are relatively recent developments, arising from a novel application of topological…

Logic in Computer Science · Computer Science 2026-02-18 Murdoch J. Gabbay

Actions on hyperbolic metric spaces are an important tool for studying groups, and so it is natural, but difficult, to attempt to classify all such actions of a fixed group. In this paper, we build strong connections between hyperbolic…

Group Theory · Mathematics 2022-07-27 Carolyn R. Abbott , Sahana Balasubramanya , Sam Payne , Alexander J. Rasmussen

In this monograph we lay the foundation for a theory of coarse groups and coarse actions. Coarse groups are group objects in the category of coarse spaces, and can be thought of as sets with operations that satisfy the group axioms "up to…

Group Theory · Mathematics 2023-07-10 Arielle Leitner , Federico Vigolo

The universal enveloping algebra U(g) of a Lie algebra g acts on its representation ring R through D(R), the ring of differential operators on R. A quantised universal enveloping algebra (or "quantum group") is a deformation of a universal…

Quantum Algebra · Mathematics 2007-05-23 Uma N. Iyer , Timothy C. McCune